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Drug‐Induced Up‐Regulation of Dopamine D2 Receptors on Cultured Cells
Author(s) -
Starr Stephanie,
Kozell Laura B.,
Neve Kim A.
Publication year - 1995
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1995.65020569.x
Subject(s) - dopamine receptor d2 , dopamine receptor , dopamine , receptor , drug , pharmacology , neuroscience , chemistry , biology , microbiology and biotechnology , biochemistry
Ligand‐induced up‐regulation of recombinant dopamine D2 receptors was assessed using C 6 glioma cells stably expressing the short (415‐amino‐acid; D2 S ) and long (444‐amino‐acid; D2 L ) forms of the receptor. Overnight treatment of C6‐D2 L cells with N ‐propylnorapomorphine (NPA) caused a time‐ and concentration‐dependent increase in the density of receptors, as assessed by the binding of radioligand to membranes prepared from the cells, with no change in the affinity of the receptors for the radioligand. The effect of 10 µ M NPA was maximal after 10 h, at which time the density of D2 L receptors was more than doubled. The agonists dopamine and quinpirole also increased the density of D2 L receptors. The receptor up‐regulation was not specific for agonists, because the antagonists epidepride, sulpiride, and domperidone caused smaller (30–60%) increases in receptor density. Prolonged treatment with 10 µ M NPA desensitized D2 L receptors, as evidenced by a reduced ability of dopamine to inhibit adenylyl cyclase, whereas treatment with sulpiride was associated with an enhanced responsiveness to dopamine. The magnitude of NPA‐induced receptor up‐regulation in each of four clonal lines of C6‐D2 L cells (mean increase, 80%) was greater than in all four lines of C6‐D2 S cells (33%). Inactivation of pertussis toxin‐sensitive G proteins had no effect on the basal density of D2 L receptors or on the NPA‐induced receptor up‐regulation. Treatment with 5 µg/ml of cycloheximide, on the other hand, decreased the basal density of receptors and attenuated, but did not prevent, the NPA‐induced increase. Chimeric D1/D2 receptors were used to identify structural determinants of dopamine receptor regulation. Treatment with the D1/D2 agonist NPA decreased the density of D1 and chimeric CH4 and CH3 receptors. The latter two receptors have D1 sequence from the amino‐terminus to the amino‐terminal end of transmembrane region (TM) VII and VI, respectively. CH2, with D1 sequence up to the amino‐terminal end of TM V, and thus the third cytoplasmic loop of the D2 receptor, was up‐regulated by NPA or the D2‐selective agonist quinpirole. Quinpirole treatment decreased the density of CH3 and had no effect on CH4 or D1 receptors. The different responses of CH2 and CH3 to agonist treatment suggest a role for TM V and the third cytoplasmic loop in the direction of receptor regulation.